This invention relates generally to surgical instruments and, more specifically, to an ophthalmologic surgical instrument used to correct simple retinal detachments and to a method of operation for using these instruments.
Ophthalmologists use various surgical techniques to attach a detached retina. These methods have evolved over many decades. For many years scleral buckling was the method of choice. Scleral buckling requires the controlled constriction of the sclera of the eyeball until the detached retina contacts the choroid, and the creation of a chorial-retinal scar to close the retinal tear and reattach the retina. A silicone band, for example, may be wrapped around the eye. When the band is threaded under the eye muscles and tightened, the sclera of the eye buckles slightly. This buckling brings the choroid and retina together. The retina is then sealed to the choroid using laser or cryotherapy method for creating the choroid-retinal scar. Compression of the eye has obvious drawbacks including increased intraocular pressure, discomfort, trauma to the eyeball, and visual disturbances. Because it is difficult to control the compression of the eye, the technique exhibits variable results.
A relatively recent procedure includes the use of a vitrectomy system in retina surgery. A vitrectomy probe is designed to cut and remove vitreous and other material such as blood, lens remnants, and iris tissue. Generally, vitrectomy probes contain a hollow tube rotated or oscillated against an outer tube. The inner tube is driven by a small motor or by pneumatic pressure. The outer tube has an aspiration port. A cutting edge is located near the distal end of the inner tube. Tissue is drawn into the aspiration port where it is severed by the cutting edge of the oscillating inner tube and sucked into the port by vacuum, and collected in a reservoir. Many of these devices have an irrigating port through which solution is introduced inside the eye. When treating a detached retina with vitrectomy, solution is introduced inside the eye while the vitreous traction to the retina is simultaneously removed. Removal of the vitreous traction relieves its adhesion to the retina thereby allowing the retina to move toward the choroid and adhere. Furthermore, in complicated cases, the solution is introduced into the eye to lavage the retina and help remove tissue. A second instrument, such as a cryocoagulation instrument, is inserted behind the eye to attach the retina.
The vitrectomy procedure has notable drawbacks. For example, The vitrectomy probe that delivers solution is, by necessity, large. The probe must be large enough to accommodate a fluid flow tube or cannula having a bore of sufficient dimensions to allow the free flow or passage of an appropriate irrigating solution such as saline solution. Because of probe size, a relatively large incision must be made to accept the probe. Invasive procedures with large bore probes are not without risk of injury to intraocular structures. Furthermore, the incision must be sutured after procedure completion and the sutures later removed. There are other associated risks with the procedure such as increased risk of infection, increased pain, patient discomfort, visual disturbances and a relatively high degree of surgical failure.
Smaller vitrectomy probes, having only the aspirating and cutting portions and no solution administration cannula, have been used. The surgeon must, however, introduce the vitrectomy probe into one incision and introduce a second irrigating cannula through another incision to provide the flow of saline or other appropriate solution. Adding a second instrument exacerbates problems associated with the surgery.
As stated above, efforts have been made to decrease the size of the probe. Separation of the fluid infusion channel from the aspiration and cutting probe allows for the overall reduction of size of each instrument. By using a separate infusion cannula, the overall size of the aspirating and cutting probe can be reduced to approximately that of a 20 gauge needle (0.90 mm). Aspirating and cutting probes, with no infusion cannula, the size of a 23 gauge needle (0.63 mm) have been reported. Theoretically, an instrument the diameter of a 25 gauge needle (0.51 mm) could be used. This type of instrument, however, could function only for aspiration and cutting and could not provide means for the infusion of a saline solution inside the eye.
Recently detached retinas have been treated with a procedure known as pneumatic retinopexy. This procedure involves intravitreal injection of an expanding gas, such as perfluoropropane (C.sub.3 F.sub.8) or sulfer hexafluoride (SF.sub.6), in conjunction with the sealing of the retinal break by laser photocoagulation or cryocoagulation. In the procedure, approximately 0.3 ml to 0.6 ml of the expanding gas is briskly injected into the eye and the patient is positioned so that the expanding gas bubble exerts a force against the retina. The surgeon utilizes a second instrument to form the scar tissue to adhere the retina to the choroid.
Although pneumatic retinopexy is an improvement over older procedures, retinopexy has significant short comings. One significant drawback is that the procedure is not effective in the presence of vitreal traction. The probe or needles used to introduce the expanding gas does not have cutting and aspirating elements. Therefore, the introduction of an expanding gas in the presence of vitreal traction can exacerbate the problem by exerting pressure on the vitreous and causing the vitreous to pull against the retina, perhaps causing other tears.
Retinopexy requires extensive pre-operative preparation. Prior to the procedure, the surgeon must lower the intraocular pressure. One method of lowering the intraocular pressure is the massage technique in which the globe is pressed firmly against the orbital wall with a cryoprobe positioned near the equator.
Furthermore, injection of the expanding gas causes a rapid increase in intraocular pressure which can result in closure of the central retinal artery. Careful monitoring of the intraocular pressure during the first few hours after injection is important since this is when the bubble of expanding gas expands rapidly. Since the gas is, by its nature, expandable, the size of the resulting bubble can be difficult to control. Moreover, the use of expanding gas makes the procedure riskier in patients suffering from glaucoma. The surgeon must relieve this occlusion of the retinal artery by draining fluid from the anterior chamber of the eye or by administering drugs such as acetazolamide (Diamox) to lower intraocular pressure by reducing the production of aqueous humor. Because of the increase in intraocular pressure, the patient must be observed for at least 1 to 2 hours after surgery, increasing post-surgical recovery time and the associated costs.
Pneumatic retinopexy is limited to treating retinal detachments or breaks in the superior 8 clock hours of the retina. This is because the patient must be appropriately positioned to allow the bubble of expanding gas to press against the retinal tear. Patients having retinal tears separated by more than 60.degree. or located in the inferior part of the retina are not good candidates for this procedure. Practically speaking, a patient having a tear in the inferior part of the retina would have to be positioned upside down to allow the bubble to contact a tear. Researchers estimate that pneumatic retinopexy can be used in only about 40% of detached retina cases. Moreover, pneumatic retinopexy is a passive procedure in that the expanding gas is injected, the patient is appropriately positioned so that the bubble migrates to the tear, and the surgeon waits for the adherance of the retina to the choria. If there is a significant amount of fluid behind the retina, the patient must be appropriately positioned and the surgeon must wait, sometimes 24 to 48 hours, for the bubble to force the fluid from behind the retina before the surgeon can preform cryocoagulation or laser photocoagulation to attach the retina. There is also a related problem, known to practioners the "fish egg" phenomenon where multiple small bubbles are introduced into the vitreal during expanding gas injection, and one or more small bubbles pass through the retinal tear and accumulate behind the retina. If multiple bubbles appear, the eye must be thumped to cause the coalescence of the bubbles. If that fails, the patient must be positioned so that the small bubbles migrate to a point opposite the tear and accumulate into one larger bubble. This can require an additional 24 hour waiting period. The delay can cause increased discomfort and inconvenience for the patient, increased costs associated with the procedure, and increased risks such as congestion of central retinal artery.
Although prior art surgical instruments and techniques represented significant advances in their time, they all suffer drawbacks. The older instruments, especially those that infuse solution simultaneously with aspirating and cutting, are relatively large. Since the use of such a probe is an invasive technique there is increased risk of infection and trauma to intraocular structures. Post-surgical suturing of the wound is required. Such complications and risks are generally unnecessary and unreasonable when performing a procedure to correct a simple retinal detachment. Furthermore pneumatic retinopexy does not allow for removal of vitreous material, is appropriate only in superior tears or detachments, can cause a rise in intraocular pressure, and can be difficult to control.
I have found that improvements in instruments and technique disclosed hereinafter enable simple retinal detachment to be treated on an outpatient basis without the effects common with known prior art instruments and procedures.